Standards provide interoperability between products, particularly with a client/server protocol.
The Internet Engineering Task Force (IETF) is one of the key organizations that defines the standards used on the internet today. Its specifications for HTTP, WebDAV and vCard form the basis of CardDAV.
RFC - these are the formal standards produced by the IETF.
Drafts - these are in-progress specifications.
The IETF has a mailing list for discussion of the CardDAV protocol.
There are a number of key standards that make up the CardDAV protocol. CardDAV is based on WebDAV which is based on HTTP and it uses vCard for contact data. The IETF has a mailing list for discussion of the CardDAV protocol.